@Henning,
Thanks for the pictures of your ISG Talisman.
The unit you have is the successor to the Talisman classic that used the Pyro-vidicon tube. It contains a BST detector array that uses a spinning shutter wheel to refresh the detector elements at IIRC 30fps. The BST detector 'sees' change rather than static temperature and needs the wheel to create such synchronised change.
BST was a very good technology but, like so many other products, the microbolometer won out on simplicity and greater investment by the US military.
I own one original Pyro-Vidicon Talisman and five of the much later BST cored WASP models which appear very similar to your unit but with a later case design.
I contacted ISG regarding the Talisman schematics and they tried to help. Sadly the classic Talisman is so old that the schematics have been lost over the years. The later BST based cameras are covered by the ITAR regulations due to the performance of the detector assembly.
Via my helpful contact in the industry I can advise that the ISG products are similar electronic design to that produced by EEV. The two were past partners
The BST detector core is a Raytheon product (hence ITAR regulations) and is a complete operational thermal camera in itself, with analogue video output. The control lines from this self contained Raytheon camera are married to a third party microprocessor board to provide the functionality that the OEM desires. Even if the third party microprocessor board fails, the Raytheon camera is still usable on its own
The schematics for the BST equipped Talismans are not available to the public and I do not have access to them. They are protected under ITAR so ISG cannot supply any internal technical information.
IMHO, the Talisman is not the greatest build quality with its very DIY appearance inside. The EEV ARGUS 1 (Pyro Vidicon) and ARGUS 2 (BST) of the same period are far superior in terms of build. I own several ARGUS 1 and 2 units as well. The Talisman saw service throughout the world and appears to have performed well in its role.
Aurora